This research project proposes to investigate the physiologic and ontogenic role of nonadrenergic inhibition (NAI) in the airway of the lung. The study will determine in vivo the influence of NAI indirectly by the alterations seen in pulmonary mechanics. The study proposes to investigate NAI in two organisms in which NAI has been demonstrated to dilate airways -- cats and normal humans. The study plan is composed of three major parts: 1) Physiologic role of NAI in vivo to bronchomotor consequences of either pulmonary reflex activation or exogenous bronchial challenge will be assessed. Localization of the NAI response within the tracheobronchial tree will be determined by the interpretation of pulmonary resistance utilizing a retrograde catheter technique. 2) Ontogeny of the function of NAI in both its influence on resting tone and its ability to reverse bronchoconstriction will be investigated postnatally to the first month of life. 3) In normal human subjects, NAI will be assessed based on the approach developed from the animal experiments using partial forced expiratory flow volume (PEFV) curves and autonomic blocking agents. The proposed research plan is an integrated approach which investigates the ontogenetic biophysical and physiologic properties of NAI. This information will provide new insights as to the significance of NAI to pulmonary mechanical function.